Transducer



June 13, 1967 L, SUPERNAW ET AL TRANSDUCER 3 Sheets-Sheet 1 Filed Sept. 13, 1965 June 313, 11967 [1 L, SUPERNAW ET AL TRANSDUCER 5 Sheets-Sheet 2 Filed Sept. 13, 1965 29% f 2 HAQE IPRONH June 13, 1967 L suPERNAW ET AL 3,325,779

TRANSDUCER Filed Sept. 13, 1965 5 Sheets-Sheet 3 (Fl G 9) (FIG. 6) (FIG. l2.) PHASE I PH/ASE FRONT I j FRONT United States Patent 3,325,779 TRANSDUCER Dwight L. Supernaw, Baltimore, and Charles R. Wilson,

Glen Buruie, Md., assignors to Westinghouse Electric Cor oration, Pittsburgh, Pa., a corporation of Pennsylvania Filed Sept. 13, 1965, Ser. No. 486,814 3 Claims. (Cl. 340-8) This invention in general relates to transducers, and more particularly to transducers for use in deep water sonar applications or the like. Sonar, transponder, beacon etc. transducers generally include an oscillatory driving element or elements for propagating acoustic energy to, and receiving acoustic energy from, the surrounding water medium. Oscillatory driving elements produce equal and opposite reactions. For optimum coupling of a maximum energy to the surrounding medium, a theoretical transducer will have the front surface of its oscillatory driving element coupled directly to the surrounding water medium and the rear surface (reaction) or other active oscillatory surfaces of the driving element coupled directly to an air backing, and preferably a vacuum backing. This type of theoretical construction can be very impractical, and sometimes impossible.

Transducers are therefore made with the oscillatory driving elements backed and supported by a pressure release material which in essence simulates an air backing so that maximum acoustic energy is radiated from the front surface of the driving elements. Popular pressure release materials include corprene, which is a cork and neoprene rubber substance, foam epoxies, onion skin paper, and foam polystyrene plastics. The unit may be placed into a housing with a covering member having the same transmission characteristics as sea water. In order to equalize and distribute pressures which will be encountered at the various oceanic depths, the housing may be filled with a liquid having the same transmission characteristics as sea water so that in essence the front surface of the oscillatory driving member is directly coupled to the sea water (through the transducer liquid, and covering member), and the back surface of the oscillatory driving element is coupled to a simulated air backing which also provides support.

At depths of several hundred feet, such transducer arrangements provide satisfactory operation in maintaining their desired characteristics and efliciency. However, at greater depths, for example, in excess of 20,000 feet where the pressure is in the order of five tons per square inch, the pressure release backing, due to the water pressure transmitted thereto through the covering member and radiating face, and transducer fluid if used, becomes compressed to a fraction of its original size. Fliud will fill the space between the back surface of the driving element and the crushed backing material. Irradic loading of the oscillatory driving element takes place, and proper transducer operation and efliciency are destroyed.

It is therefore a primary object of the present invention to provide an improved transducer which will maintain proper operation not only at shallow depths but at deep oceanic depths where the pressure encountered may be in the order of several tons per square inch.

Another object is to provide an improved transducer which eliminates the need for a pressure release medium with its limitations and inherent losses.

A further object of the invention is to provide various transducers for producing different desired beam or pattern characteristics at any oceanic depths.

Briefly in accordance with the above objects, the broad concept of the invention comprises an oscillatory driving means providing acoustic energy in a first direction and 3,325,779 Patented June 13, 1967 in a second and different direction. Acoustic reflecto1 means are provided and positioned relative to the oscillatory driving means to direct the acoustic energy in the second direction through two points of reflection to substantially adjacent the position and direction as the acoustic energy in the first direction.

The objects and the basic concept are accomplished in the present invention, one illustrative embodiment of which comprises a transducer having an oscillatory driving means located within a transducer housing and being filled with a fluid which has substantially the same transmission characteristics as the fluid medium in which the transducer operates. The oscillatory driving means has front and rear surfaces moving in the same direction, each of which produces a pressure front, or wave, herein called an acoustic signal, when the oscillatory driving means is suitably energized at an operating frequency, and conversely when operated as a receiver the oscillatory driving element will produce an electrical signal in accordance with the acoustic energy received. The use of the word transducer herein is meant to include both its use as a transmitter (projector) and receiver (hydrophone). The transducer is arranged within the housing such that the front surface of the oscillatory driving means produces a first acoustic signal which travels directly into the surrounding water medium through the fluid in the transducer housing and through a covering member having suitable transmission characteristics. The rear surface of the oscillatory driving means simultaneously produces a second acoustic signal traveling in the opposite direction as that produced by the front surface. A first acoustic reflecting surface portion is positioned behind the rear surface of the oscillatory driving means so as to reflect the rearwardly traveling second acoustic signal. A second acoustic reflecting surface portion is provided and is located relative to the first acoustic reflecting surface so as to direct the second acoustic signal reflected therefrom in substantially the same direction as the acoustic signal produced by the front surface of the oscillatory driving means.

When used as' a receiver, incoming acoustic energy strikes the front surface of the oscillatory driving means, and strikes the rear surface only after being reflected by the second acoustic reflecting surface portion and then the first acoustic reflecting surface portion.

The arrangement of the reflecting surfaces is such that the rearwardly directed second acoustic signal, which is out of phase with the first acoustic signal, impinges upon the first reflecting surface is reflected to the second reflecting surface, is again reflected, and comes out substantially adjacent the forwardly directed first acoustic signal. The reflecting surfaces are constructed and arranged so that the phase front of the rearwardly directed and twice reflected second acoustic signal, after a total distance of travel of is adjacent to the first acoustic signal and may be in phase, leading or lagging therewith or may be in a curved surface to produce a total signal for a specific pattern requirement. A is the wavelength of the acoustic signal in the housing fluid and n is an odd integer, and for practical purposes equal to 1.

Depending upon'the configuration of the oscillatory driving means used as the active element, the first and second acoustic reflecting surfaces may take on various shapes. For a generally cylindrical or annular oscillatory driving means operating in the hoop mode, the refleeting surfaces may include a plurality of conical members axially aligned with mating apexes and bases. With the hoop mode oscillatory driving means arranged so that its central axis falls on the central axis of the conical members, the acoustic signals provided by the rear or inner surface are reflected from first and second cone members and are projected in phase, and adjacent to, the acoustic signals provided by the front or outer surface of the driving means.

For a disc-type oscillatory driving means operating in the umbrella mode, the arrangement may be such that the driving means is positioned at the apex of a conical member which in turn is situated within a dish-type member, the surface portion of the dish-type member and the surface portion of the conical member forming two reflecting surfaces.

For a bender bar or place type of oscillatory driving means, two adjacent grooves may be provided defining properly sloped acoustic reflecting walls, with the oscillatory driving means being positioned along the ridge that is formed by the configuration.

Where it is desired to shape the beam pattern produced by the transducer or to correct for minor lobe distortions, or the like, the path length of reflected acoustic signals may be varied slightly to encompass a U2 reflected phase front slightly leading or lagging the acoustic source oscillatory surface of the first signals.

The above stated as well as further objects, advantages, and features, will become apparent upon the reading of the following detailed specification taken in conjunction with the drawings in which:

FIGURE 1 is an isometric view, partially in section, of a transducer according to the teachings of the present invention;

FIG. 2 is a cross-sectional view of the transducer of FIG. 1; 7

FIG. 3 is an isometric View, partially in section, of an other embodiment of the present invention;

FIG. 4 is an isometric view, partially in section, other embodiment of the present invention;

FIG. 5 is a schematic illustration of the reflecting surfaces of the transducer of FIG. 4;

FIGS. 6 through 12 illustrate cross-sectional views of various transducer reflecting means and orientations of driving elements;

FIG. 13 illustrates the sectional build-up of a particular transducer; and

FIG. 14 illustrates design.

Referring now to FIGURE 1, there is shown a transducer having a housing member which is shown in cross section to be substantially W-shaped in defining two sides 15 and 16 and a central peak portion 12 having sides 13 and 14. Side 16 lies in a first acoustic reflecting surface portion 16 (not shown) extending the length of the transducer; side 13 lies in a second acoustic reflecting surface portion 13 extending the length of the transducer; side 14 lies in a third acoustic reflecting surface portion 14 (not shown) extending the length of the transducer; and side 15 lies in a fourth acoustic reflecting surface portion 15.

An oscillatory driving element 20 is provided and is located and secured in the vicinity of the apex of peak portion 12. In other words, the oscillatory driving element 20 extends in a direction defined by the intersection of surfaces 13' and 14. The oscillatory driving element 20 is operable, upon proper excitation in a well known manner, to provide a first acoustic signal from the top or front surface 22, and to provide a second acoustic signal from the bottom or rear surface 23. The driving element 20 is operated in a bender mode, defined by the top surface 22 and bottom surface 23 moving in the same direction upon excitation. The first acoustic signal, emanating from the top surface 22 has a certain wavelength as determined by the operating frequency and surrounding medium. This first acoustic signal is schematically illustrated by the arrows labeled F. The

of ana modification of the transducer second acoustic signal emanating from the rear surface 23 has the same wavelength, however since the top and bottom surfaces 22 and 23 are traveling in the same direction, the second acoustic signal will be out of phase with the first acoustic signal from the top surface. The rearwardly directed second acoustic signal is indicated by the arrows labeled R.

The second acoustic signal from the rear surface 23 strikes the reflecting surfaces 13 and 14' and is reflected over to surfaces 16 and 15. The reflected acoustic signal is schematically designated R; After reflection from surfaces 16 and 15', the acoustic signal travels in substantially the same direction as the first acoustic signal, and is labeled R". The acoustic reflecting surfaces are arranged in a manner that the rearwardly directed second acoustic signal travels a total distance of M2 from the rear surface 23 to the plane of the front surface 22 ()t is the wavelength of the acoustic signal) and emerges adjacent to the first acoustic signal and substantially in phase therewith since, in effect, the 2 distance that it travels operates as a 180 acoustic delay line. In FIG- URE 1, this is accomplished by having the first and second acoustic reflecting surfaces 16' and 13 meet at a right angle, and third and fourth acoustic reflecting surfaces 14 and 15 meet at a right angle, with the distance from the meeting point to a plane midway between surfaces 22 and 23 being A/ 4. The oscillatory driving element is positioned relative to the reflecting surfaces such that the second acoustic signal is directed only toward the second and third reflecting surfaces 13' and 14'. In other words, in a plan view of the apparatus, the sides of the oscillatory driving element 20 would not extend past the intersections of the first and second, and third and fourth reflecting surfaces.

In a practical construction the central peak portion 12 includes a support upon which the oscillatory driving element rests. FIG. 2, which represents an end view in section of the transducer of FIG. 1, illustrates this in more detail. The sides of the central peak portion 12 do not actually meet. The central peak portion 12 is seen to include a support portion 17 upon which the driving element rests and is secured thereto by means of, for example, screw member 18. The support portion 17 has a certain width designated X and this portion of the oscillatory driving element remains inactive. The total width Y of the oscillatory driving element therefore includes an inactive portion X and two active portions. The line 19 represents the phase front of the second acoustic signal after a total distance of travel of a half wavelength and is herein termed the 2 phase front, and it is seen that the M2 phase front 19 is even with the top surface of the oscillatory driving element 20. To accomplish this, it may be mathematically demonstrated that the horizontal distance from the central axis of peak portion 12 to the intersection of the two reflecting surfaces is the support width X. The oscillatory driving element 20 therefore has a dimension perpendicular to the central axis of no more than M 2 plus the support width X. In FIG. 2 the second acoustic signal and phase front 19 has only been drawn for one half of the transducer. It is to be understood that the same considerations are applicable to the other half.

Referring back to FIG. 1, the transducer is filled with a transducer fluid, in a well known manner, and is contained by covering member 25 which is made of a material having similar transmission characteristics as the fluid medium in which the transducer operates. For sea water operation, the covering member 25 may be a rubber known as Rho-C rubber and the fluid within the transducer may be a high grade castor oil. For extreme depths, for instance in the order of 20,000 feet or greater, the fluid within the transducer may be one which more closely approximates that of sea water at the particular pressure and temperature of the operating depth. Silicone base fluids are applicable.

The second acoustic signal from the rear surface 23, and represented by arrows R, strikes the reflecting surfaces 13' and 14 at a certain angle to the normal to these surfaces. From a theory of stress waves in two adjacent mediums, it may be demonstrated that there is a critical angle 0 (measured from the normal to a surface) above which a wave hitting the surface will be totally reflected, and below which the wave will not be totally reflected 'but will set up a stress in the second medium. The critical angle 0 is governed by the characteristics of the two adjacent mediums with respect to sound velocity therein. In the figures herein, the first medium is the transducer fluid, and the second medium is the reflecting member. With a reflecting member of, for example stainless steel, critical angle 0 is in the order of 19 and the transducers herein are designed such that the second acoustic signal strikes two acoustical reflecting surfaces in sequence at an angle greater than the critical angle 6' so that total reflection takes place.

The oscillatory driving element 20 is basically illustrated as a crystal, however, various different types of piezoelectric, pieZo-ceramic, magnetostrictive, etc. types ofjactive elements may be utilized, either as a single strip, as illustrated, or else as a plurality of end-to-end elements.

Other arrangements of the transducer of the FIGURE 1 include systems wherein the general configuration shown, is repeated in side-by-side fashion so that in essence there are parallel elongated oscillatory driving elements.

In side looking sonar applications, it is desirable that the beam width in a plane perpendicular to the bottom be extremely large, for example, approaching 90, and that the beam in a plane substantially parallel to the bottom be less than one degree. With the oscillatory driving element 20 having a longitudinal dimension of many wavelengths, the transducer of FIGURE 1 finds particular application in side looking sonar systems where operation at .deep oceanic depths are desired. Another type of 'beam pattern which is sometimes desired is a so-called Searchlight beam pattern and to this end reference should now be made to FIGURE 3.

In FIGURE 3, the transducer includes a housing member also having a W-shaped cross-section defining a central peak portion 32 and sides 34 and 35. In FIGURE 3 however, the sides of the central peak portion 32 are surface lines of a conical member 37 defining a first acoustic reflecting surface portion, and the lines 34 and 35 lie in the same second acoustic reflecting surface portion 39, the sloping character of which may be defined by a conical surface, which meets the conical member 37 at intersection line 41 which lies at the valley points of the -shaped cross section.

Oscillatory driving element 44 is positioned at the top of member 32 and includes a front surface 45 for providing, upon proper excitation, a first acoustic signal generally designated by the arrows F, and a rear surface 46 for simultaneously providing a second acoustic signal generally designated by the arrows -R and being 180 out of phase with the first acoustic signal, The oscillatory driving element is circular and operates in the umbrella mode. The transducer is filled with a transducer fluid and retained by covering member 48 which may also be of the Rho-C rubber variety.

The principal of operation of the transducer of FIG URE 3, is similar to that of FIGURE 1 in that the second acoustic signal is initially reflected (R), from a first acoustic reflecting surface 37 and is again reflected '(R"), off of a second acoustic reflecting surface 39 to emerge adjacent to and substantially in phase with, the first acoustic signal. The total distance traveled by the second acoustic signal from the rear surface 46 until it emerges adjacent to and in phase with the acoustic signal at the top surface 45 is in the order of M2 In order that the second acoustic signal from the rear surface 46 does not strike the second acoustic reflecting surface 39 first, the diameter of the oscillatory driving element 44 is chosen to fall entirely within an upward projection of the intersection line 41. The cross sectional view illustrated in FIG. 2 is also applicable to the transducer of FIG. 3. The oscillatory driving element 44 would be located on and secured to a support portion which would provide an inactive surface portion of X. Whereas in FIG. 1, X represented a width, in FIG. 3 the X would be a diameter, and whereas Y represented a width, in FIG. 3, Y would represent the diameter of the oscillatory driving element 44. The total diameter therefore would be However, for an in phase condition the active portion of the oscillatory driving element would be no more than M2.

The conical member 37 is axially aligned with the conical surface 39 so that the second acoustic signal directed toward the conical member 37 is reflected therefrom, strikes the conical surface 39, is reflected therefrom and is thereafter directed in the same general direction, and substantially in phase with, the first acoustic signal to produce a substantially searchlight type beam. For an embodiment of the invention, in which various omnidirectional beams may be produced reference is now made to FIGURE 4.

The structure of the transducer of FIGURE 4 is somewhat symmetrical about a central horizontal plane through the transducer and symmetrical component counterparts are labeled with primed numerals. The transducer of FIGURE 4 includes an oscillatory driving element 5%), having a top surface 52, a bottom surface 53, an inner generally cylindrical surface 54, and an outer generally cylindrical surface 55. The oscillatory driving element 50 operates, upon proper excitation, in the hoop mode wherein the inner and outer surfaces 54 and 55 travel in the same radial direction.

A first acoustic reflecting surface portion 58 is defined by a first conical member 59, and a second acoustic reflecting surface 61 is defined by a second conical member 62. Since FIGURE 4 is an isometric view partially in section, the conical members defining the acoustic reflecting surfaces have been redrawn in FIGURE 5 so that they may be easily viewed, and explained. Basically, the conical members 59 and 62 have the same central axis and are axially aligned apex to apex. FIGURE 4 and FIGURE 5 illustrate the conical members as having apexes communicative with one another. The radial distance from the valley of their intersection, to a point midway between surfaces 54 and 55 is M4. The conical surfaces form a valley around the transducer axis. The length of the oscillatory drive element is M4. The combination of the oscillatory drive element 50 in conjunction with the first and second reflecting portions 58 and 61 will provide an omnidirectional pattern in a plane perpendicular to the transducer axis, well known as the horizontal plane. The addition of the symmetrical portion illustrated by primed reference numerals serves to modify the pattern in a plane of revolution common to the transducer axis, well known as the vertical plane. The width of the vertical pattern decreases as the total effective radiating face of the transducer decreases with respect to A.

With the axially aligned conical members 59, 62, 62 and 59 being separate pieces, as illustrated, they may be positioned in place by an axial retaining member 64.

The conical member 59 is surrounded by the oscillatory driving element 50 which has its lower surface 53 abutting seating means 66 in the vicinity of the base portion of conical member 59. The oscillatory driving element 50 has its inner and outer cylindrical surfaces 54 and 55 extending in the same direction as the central axis of the conical member 59 and extends a distance no more than the meeting of conical members 59 and 62. Basically, as shown in FIG. 5, the conical members 59 and 62 have surface lines (the outermost surface lines are illustrated) which meet at an angle. Even if the conical members 59 and 62 were separated from one another, the surface lines, or projections thereof, would still meet at an angle. The sides of the oscillatory driving element do not extend past the meeting of the conical surface lines. Seating means 69 abuts the top surface 52, and the oscillatory driving element is held in place by the retaining ring 71 in conjunction with posts 72 secured to an end section 74 forming a closure means and which may or may not be integral with the conical member 59.

The oscillatory driving element 50 is operative in the hoop mode, that is, upon proper excitation the inner and outer surfaces 54 and 55 both move in the same direction radially of a central axis with the outer surface 55 providing a first acoustic signal of a certain Wavelength and generally illustrated by the arrow F, and the inner surface 54 providing a second acoustic signal of the same wavelength but 180 out of phase and generally designated by the arrow R. The second acoustic signal is reflected off of the first acoustic reflecting portion 58 (R') and once again off of the second acoustic reflecting surface portion 61 and emerges (R") adjacent to, and substantially in phase with, the first acoustic signal F.

The oscillatory driving element 50 in conjunction with the first and second acoustic reflecting surface portions 58 and 61 form an operative transducer or transducer element providing an omnidirectional pattern in the horizontal plane and a donut shaped or cardioid type pattern in the vertical plane. Increase in the axial length of the transducer with respect to A, flattens the width of the cardioid pattern.

As a variation, the components labeled with primed reference numerals such as the oscillatory driving element 50' and its associated reflecting means may be of a different size and operate at a different frequency than their unprimed counterparts to form a dual or multiple frequency transducer in a single housing. The assemblies common to each frequency may function independently. Their vertical patterns, individually, will be a function of their individual lengths with respect to A at each frequency and their horizontal patterns will be omnidirectional.

For a broad band transducer, multiple oscillatory means 50, 50 50" and their associated reflecting means may be coaxial assemblies of different sizes and operate at different frequencies common to some part of the total broad frequency response requirement of the transducer.

The transducer configuration of FIGURE 4 is actually a plurality of pairs of conical members axially aligned apex to apex, with the pairs arranged base to base, and with an oscillatory driving element surrounding only one conical member of each pair. In other words, the elements with primed reference numerals form a mirror image of the unprimed reference numerals and operate in the same manner. The beam pattern provided by the transducer of FIGURE 4 is omnidirectional in the horizontal plane and more specifically forms somewhat of a donut shaped beam. This beam may be flattened out by providing additional axially aligned basic transducer elements which in turn may be mirror images of the configuration illustrated in FIGURE 4, or FIGURE 5.

Means to provide a rigid structure include elongated supports 76 which pass through retaining rings 71 and 71 and are fastened to the end sections 74 and 74'. Covering member 78 is secured to the lower and upper end sections 74 and 74' and surrounds the transducer elements. Covering member 78 may be a RhoC rubber. The internal cavity of the transducer is filled with transducer fluid through aperture 80 which may be closed by plug 81 threadedly secured to the end section 74.

In FIGURE 1, the first and second acoustic reflecting surface portions were planar. In FIGURE 3, the reflecting surfaces took on the form of a first, conical surf-ace and a second conical surface inverted with respect to the first conical surface. In FIGURE 4, the second acoustic signal is brought out adjacent to and in phase with the first acoustic signal by mutually opposing conical surfaces. If it is desired, the reflecting surface portions may be somewhat varied for desired pattern changes, minor beam lobe corrections or to accommodate for different physical size configurations. Various embodiments are illustrated in FIGS. 6 through 12.

Each of the FIGURES 6 through 12 shows an oscillatory driving element, and reflecting means. For ease of explanation, the upper surface of the oscillatory driving element or driver will be termed the front surface and the lower surface will be termed the rear surface. The left-most reflecting surface will be termed the first reflecting surface and the right-most reflecting surface will be termed the second reflecting surface although in actuality since the figures are in cross-section, the lines representing the reflecting surfaces are actually surface lines. Since the front and rear surfaces of the oscillatory driving element travel in the same direction upon proper excitation, FIGS. 6 through 12 are illustrated of operation in the bender, umbrella or hoop mode and the first and second reflecting surfaces may be actually planar, or conical, or other curvilinear solids.

FIG. 6 represents the embodiments illustrated in FIGS. 1, 3 and 4. The second acoustic signal from the rear surface of the driving element is reflected twice and after a total distance of travel of M2 lies in some surface or boundary termed the M2 phase front. The driving element is M4 and the distance from a plane midway between the front and rear surfaces to the valley point where the first and second reflecting surfaces meet is M4, the configuration providing a M2 phase front which is even with and forms a continuation of the front surface of the driving element. In other words, the reflected acoustic signal is in phase with the first acoustic signal.

In FIG. 7 the arrangement is such that the M2 phase front is also even with the front surface of the driving element, however the driving element is less than M4. Since the distance from a plane midway between the front and rear surfaces of the driving elements is M4 away from the valley point, the driving element is disposed at a slight distance x above the first reflecting surface.

In FIG. 8, the M4 driving element is disposed above the first reflecting surface such that the distance from a plane midway between the front and rear surfaces to the valley point is greater than M4, but less than M2, to produce the M2 phase front as illustrated and which represents a phase lag since it is below the front surface of the driving element.

In FIG. 9' the driving element is less than M4 as is the distance from a plane midway betwen the front and rear surfaces to the valley point, to produce a M2 phase front which is leading in phase since it is above the top surface of the driving element.

The effects of FIGS. 8 and 9 may be combined as illustrated in FIG. 10 by providing a second acoustic surface which is step cut to provide both leading and lagging M2 phase fronts.

In FIG. 11 the driving element is equal to or less than M4 and is located at a distance x above a point of the first reflecting surface. The second reflecting surface is curved in a manner that the M2 phase front is even with the front surface of the driving element and gradually curves downwardly to approximately meet the second reflecting surface in a curvilinear fashion.

FIG. 12 illustrates a modification of FIG. 11 and includes a first reflecting surface at an angle of less than 45 from the vertical. The second reflecting surface is curved in a manner that the M2 phase front extends from the front surface of the driving element down to a point lower than that illustrated in FIG. 11.

Many of the embodiments illustrated in FIGS. 6 through 12 may be combined to form a single unit. One such unit is illustrated in FIG. 13 in cross sectional view. The reflecting surfaces are conically shaped as in FIG. 4 and the right-most reflecting surface is the solid developed by rotating a curved line about an axis. The left-most driving element and associated reflecting surfaces correspond to that illustrated in FIG. 9; the middle driving element and associated reflecting surfaces correspond to that illustrated in FIG. 6; and the right-most driving element and associated reflecting surfaces correspond to that shown in 'FIG. 12.

Accordingly, in the various figures there have been illustrated transducers having active elements which provide first and second acoustic signals 180 out of phase with each other and in which the second acoustic signal is reflected off of two acoustic reflecting surfaces at an angle greater than the critical angle to emerge adjacent to and substantially in phase with the first acoustic signal, with the active element being out of the path of the reflected acoustic signal.

A typical transducer such as illustrated in FIG. 4 Was constructed and designed to operate at a frequency of 6.72 kc. At 6.72 kc. the wavelength in the transducer fluid was 8.8 inches The oscillatory driving element 50 was a lead-zinc-titanate ceramic and had a mean diameter of 5 inches with a wall thickness of 3 of an inch and operated in the hoop mode. The distance from the bottom surface 53 to top surface52 was 2.2 inches, a quarter wavelength. Overall lengthof the configuration from the bottom sur face 53 of oscillatory driving element 50 to the bottom surface 53' of oscillatory driving element 50' was a full wavelenth A, or 8.8 inches.

In FIGS. 8 and 9, there is shown different constructions for providing lagging and leading 2 phase fronts. This may also be accomplished .by varying the frequency. For example, the transducer design for 6.72 kc. had a half wavelength of 4.4 inches. If that same transducer were operated at a frequency of, for example, 10 kc. the half wavelength M2 would be in the order of 3 inches. Conversely, by operating at a frequency below 6.72 kc. a phase lead may be provided. Thus, it is seen that for a particular transducer having certain dimensions, the active oscillatory driving element may be a quarter wavelen th, greater than a quarter wavelength, or less than a quarter wavelength representing operation at, above, or below a design operating frequency.

In FIGURE 14, an oscillatory driving element 95 is represented in side view and may be a section through a hoop mode transducer or if the sides 96 and 97 are supported, the driving element may be rectangular or round such as illustrated in FIGURES 1 and 3. Reflecting means is disposed behind the rear surface 102 and includes a first reflecting portion 105 and a second reflecting portion 106 at an angle thereto. The distance from the rear surface 102 to the valley point at which thetwo surfaces 105 and 106 meet is M4. The initiating second acoustic signal provided by the rear surface 102 therefore strikes the reflecting means on the first reflecting surface portion 105, is reflected to the second reflecting surface portion 106, and is therefore reflected back to the rear surface 102. In a similar manner, the acoustic signal also strikes the second reflecting surface portion 106, is reflected to the first reflecting surface portion 105 and thence back to the rear surface 102. The two surfaces 105 and 106 meet at a 90 angle and since the distance from the rear surface 102 to the valley point is M4, the acoustic signal represented by the arrow R travels a distance of M2 and is totally reflected through the delay line, in phase with the initiating acoustic signal. The reflecting means is disposed relative to the rear surface 102 in a manner that all of the second acoustic signal impinging upon it does so at an angle greater than 6, the critical angle, so that total reflection takes place.

Although the present invention has been described with a certain degree of particularity, it should be understood that the present disclosure has been made by Way of example and that modifications and variations of the present invention are made possible in the light of the above teachings.

What is claimed is:

1. A transducer comprising:

(A) an oscillatory driving element (1) having. front and rear surfaces and (2) operable to provide first and second acoustic signals from said front and rear surfaces, respectively, upon proper excitation;

(B) first and second acoustically reflecting surfaces positioned relative to said oscillatory driving element that,

(1) said second acoustic signal strikes said first and second acoustic reflecting surfaces in sequence and,

(2) said second acoustic signal after a total distance of travel of where n is an odd integer and A is the wavelength of the acoustic signal, lies in a phase front;

(C) said reflecting surfaces providing a resultant phase front which has a surface line extending away from said oscillatory driving element in curvilinear fashion;

(D) said oscillatory driving element being out of the path of said phase front.

2. A transducer comprising:

(A) an oscillatory driving element having first and second opposed surfaces;

(B) a first acoustic reflecting member positioned rearwardly of said second surface;

(C) a second acoustic reflecting member;

(D) a cross section through both said first and second acoustic reflecting members defining 1) a first surface line lying on the surface of said first acoustic reflecting member, and

(2) a second surface line lying on the surface of said second acoustic reflecting member;

(B) one of said surface lines being a straight line and the other of said surface lines being a curved line;

(F) said first and second surface lines meeting at a point;

(G) said oscillatory driving element, if energized at an operating frequency, f for use as a transmitter, providing acoustic energy from said first and second opposed surfaces of said oscillatory driving element, and positioned in a manner that the energy from said second surface strikes said first and second acoustic reflecting members in sequence and;

(H) if used as a receiver, incoming acoustic energy strikes said first surface, and strikes said second surface of said oscillatory driving element only after sequential reflection from said second and said first acoustic reflecting members.

3. A transducer comprising:

(A) means defining first and second conical surfaces facing one another and each being on the same central axis;

(B) a cross section through said conical surfaces along 11 said central axis defining surface lines which meet at an angle;

(C) an oscillatory driving element having upper and lower surfaces, and inner and outer cylindrical surfaces;

(D) said oscillatory driving element being operative to provide acoustic energy of a certain wavelength upon proper excitation;

(B) said oscillatory driving element being arranged with its lower surface surrounding a base portion of said first conical surface and having its inner and outer cylindrical surfaces extending in the same direction as said central axis; and

12 (F) the effective height of said oscillatory driving element being no more than )\/4.

References Cited UNITED STATES PATENTS 6/1935 Hayes. 7/1956 Rymes. 

1. A TRANSDUCER COMPRISING: (A) AN OSCILLATORY DRIVING ELEMENT (1) HAVING FRONT AND REAR SURFACES AND (2) OPERABLE TO PROVIDE FIRST AND SECOND ACOUSTIC SIGNALS FROM SAID FRONT AND REAR SURFACES, RESPECTIVELY, UPON PROPER EXCITATION; (B) FIRST AND SECOND ACOUSTICALLY REFLECTING SURFACES POSITIONED RELATIVE TO SAID OSCILLATORY DRIVING ELEMENT THAT, (1) SAID SECOND ACOUSTIC SIGNAL STRIKES SAID FIRST AND SECOND ACOUSTIC REFLECTING SURFACES IN SE QUENCE AND, (2) SAID SECOND ACOUSTIC SIGNAL AFTER A TOTAL DISTANCE OF TRAVEL OF 